The field of this invention is the separation of fatty acid esters. The separated esters are useful, for example, as chemical intermediates in the manufacture of fatty chemical derivatives.
Fractional distillation is the most common method now being used commercially to separate fatty acid esters. This unit operation separates on the basis of chain length only. It does not separate on the basis of unsaturation.
Fractional solvent crystallization, which is used to separate fatty acids on the basis of unsaturation, is not economic for fatty acid esters. Temperatures of minus 50.degree. F. to minus 70.degree. F. and lower would have to be used, the crystals would be very fragile, and there would be a mutual solubility between unsaturate components; this provides a very expensive process for a substantially incomplete separation.
Urea adduction is another uneconomic process for separating fatty acid esters. This consists, for example, of admixing the esters to be separated with urea and acetone and cooling whereby the urea forms a crystal cage around the highest melting point esters (usually the saturates). Recovery of ester from the adduct is difficult. Moreover, this process is not as effective for separating one unsaturate from another. Furthermore, this process is difficult to adapt to continuous operation.
It is an object of this invention to provide a process for separating fatty acid esters according to degree of unsaturation which does not require low uneconomic temperatures or difficult recovery of product and which can separate one unsaturate from another and which is readily operated on a continuous basis.